Oh dear, it is time for more humble pie. I had a close look at the head on my 1946 Model 18. You are correct Peter. The oilway is drilled all the way through To the outside of the head, but the outermost portion was then blanked off by driving in a short steel plug!The irony of all my previous comments is that I actually removed this plug by drilling is out, to allow cleaning out of the head oilways. I then tapped it out to screw in a blanking plug. Only excuse is, it was about 15 years ago and Thus long forgotten. I am guessing that your head has had similar treatment and the oilway plugged with a good dollop of silicon.Sorry for my errors,Cheers, Bob.

Just to be sure, or as sure as possible about all this:My '47 iron cylinder head has 3 oil gallery drillings from the off side to valve guides.The metered one to the inlet is not a problem.But there are actually 2 drillings directed to the exhaust valve guide:

1) forward from the ex pushrod tube is blanked off with a metal plug and has no drilling to feed oil down into it from the rocker box.2) the one I have been asking about, is the middle drilling with no plug and no internal thread. This has a drilling to feed oil from the rocker box.

I'm mentioning this as it was said that the outer end of the exhaust oil gallery has a metal plug. and as I say, the most forward gallery (presumably a relic from an earlier model) has just such a plug.So I just want to be sure there is no confusion. I will hold off from plugging the outer end of the gallery that has the oil feed until I am sure.

I have a photo, but not being at all adept with computors, I do not seem to be able to attach it. I can probably email the photo to somebody if they could attach it to this thread, it could help others.

Being part Irish, nobody can be offended if I say, "To be sure, to be sure!"

On a run at the weekend I saw an iron head Matchless with exactly the same arrangement and the middle oil gallery was blanked off as I expected it should be. The owner who had some experiance of the things, thoroughly agreed. Also looking over an article in Real Classic revealed a picture in which the blanking plug was there. So I am now quite sure how to proceed.But where did the blanking plug go?I know that the previous owner had work done on the engine including rectifying a sticking exhaust valve. Maybe the plug was removed to check the oilway was clear, and some how, didn't get reffitted.I'll never know, but its the only explanation that makes much sense.